Hello to all,
Im trying to desing a VHF amplifier for ose OFDM modulation, before apliyying predistortion techniques I have to improve the linearity the best possible. I was tried these 2 transistor from freescale (with well knowledge of efficiency vs linearity compromise): MRF6V2300, and Push-Pull 6VP2600H using 50V and differents IdQ.
I know how to well mach input/output and tunning the polarization gives me differents spectral regrowths, but the fact is that I can't achieve the specified performances in the datasheet for a 6Vp2600H nor MRF6V2300.
All this it gives me very poor linearity/efficiency performance compromise. I know for example that there are some amplifiers with pair of 6VP2600H that achieves 200Watts rms with 25% eff and shoulders < -30dbc, with this specs I can only achieve ~ 20-25 dBc and eff not better than 20%...
My desing process starts with an arbitrary point of polarization (one of the specified in the datasheets, frequently that gives the better linearity performance), then I try to optimize Input network, later to optimize the output matching network... in this process some re-tunning of input matching network may be needed... (Im not using design software, I have VNA, spectrum analyzer )
When I achieve the better efficiency performance, I try to optimize the linearity...
So my questions are:
What are the steps did you make for achieve the desired performances?
Did I something wrong? what?
Thanks In advance